This invention pertains to a heating apparatus. Heat treatment of such target objects as semiconductor wafers is involved among the numerous processes in semiconductor device manufacturing. Examples of such treatment are oxidation treatment, scattering treatment, CVD treatment, epitaxial treatment, doping treatment and others.
The heating apparatus employed for such heat treatment typically consists of a processing vessel such as a reaction tube, in which the semiconductor wafer target objects are placed, heat insulating material enclosing this processing vessel, and a heat generating means located at the inner wall of this heat insulating material.
Conventionally, ceramic fiber is utilized as this heat insulating material, while the heat generating means typically consists of Kanthal (tradename) wire, an alloy of iron (Fe), chromium (Cr) and aluminum (Al) or similar resistance type heat generating material.
Recently, a heating apparatus capable of high speed temperature increase and decrease has been sought for the purpose of improving semiconductor device manufacturing efficiency. However, since a heat generating means composed of Kanthal wire has a low permissible current density, achieving a sufficiently fast temperature rise is difficult.
Studies were undertaken by the inventors involving the use of molybdenum disilicide (MoSi.sub.2) as a material for the heat generating means. If MoSi.sub.2 is used, the heat capacity is small and high speed temperature rise is possible.
MoSi.sub.2 is difficult to oxidize in comparison to Kanthal and other conventionally used heat generating means. The power making amount (watts or amperes per square cm) is about 10 times, enabling large heat application. But conversely, sudden heating subjects the insulating material to large heat shock and, for example, when using a double insulator in which the outer density is small and the inner density is large, cracks are easily produced.
Consequently, when using a heat generating means made of MoSi.sub.2 for repeated processes that involve high speed temperature rise, cracks are easily produced in a ceramic fiber insulator due to spalling and powdering occurs due to thermal deterioration of the materials composing the insulator.
Another problem occurs in the cooling process required after semiconductor wafer heat treatment. Cooling medium is employed in order to quickly reduce the temperature in the processing vessel heated area. But when this is repeated, the insulator material deteriorates, peeling occurs and particles are produced which form a cause of contamination.
Chemical reaction occurs at the points of contact between a heat generating means formed from MoSi.sub.2 and an insulator made of ceramic fiber, the problem of open wiring is encountered.